1. Field of the Invention
The present invention relates to a transfer apparatus for transferring measurement data detected by a sensor in various industrial machineries.
2. Description of the Related Art
In various industrial machineries, various physical amounts are detected by a sensor attached to an industrial machinery, and detection signals thereof (analog signals) are transferred to a controller of the industrial machinery directly or via an amplifier. On the other hand, an A/D converter, which is provided inside the controller, converts the received detection signals into digital signals, and the controller utilizes the same for controlling.
For example, in an injection molding machine, a pressure applied to an injection screw for detecting a resin pressure inside a heating cylinder is detected by a sensor such as load cell, and a detection signal thereof (analog signal) is transferred to a controller for controlling the injection molding machine. On the other hand, an A/D converter, which is provided inside the controller, converts the received detection signal into a digital signal, and the controller utilizes the digital signal converted (pressure information) for injection control (see Japanese Patent Application Laid-Open No. 9-76318).
The analog signal measured by the sensor is digitally sampled in the A/D converter to be converted into a digital signal, and the digital signal converted is serially transferred to the controller. On the other hand, the digital signal received from the sensor is subjected to a filtering processing in a digital filter for noise removing, and the controller utilizes the same.
When the sensor output is transferred to the controller in the state of analog signal, there is a problem that noise occurring along with the transfer of analog signal is easily mixed in a sensor signal.
At the sensor side, the A/D converter digitally samples a sensor detection signal to convert it into a digital signal, and transfers the same to the controller. On the other hand, at the controller side, the transferred digital signal is subjected to a filtering processing for noise removing, and is then utilized. In this case, the sensor signal received by the controller is a signal every transfer cycle. Finally, a cycle at which the signal detected by the sensor is digitally sampled in the A/D converter is limited to the transfer cycle. It is useless that A/D conversion is performed at a sampling cycle shorter than the transfer cycle, and an accuracy of the sensor signal which can be grasped by the controller is determined by the transfer cycle.
Since the filtering processing is performed by the digital filter for noise removing at the controller side, the filtering processing is realized only after the serial transfer is performed a predetermined number of times or more. Thus, there is a problem that it takes much time after the sensor detects the physical amount until the controller utilizes the sensor output signal, causing a delay.